1. Field Of The Invention
The present invention relates to a record reproducing method for a recording medium and a reproduction apparatus thereof.
More particularly, the invention relates to a record reproducing method and a reproduction apparatus thereof for recording a video signal and a digital audio signal superposed on a recording medium and reproducing them.
The present invention also relates to a video disk record reproduction system which is optimized to be applied to an optical video disk.
2. Background Art
A hi-fi video disk on which a digital audio signal with a compact disk (CD) format is recorded by superposition on a video disk is well-known as a recording medium on which a video signal and a digital audio signal are recorded as superposed signals. A record spectrum of this hi-fi video disk is shown in FIG. 1. In the figure, the portion marked A denotes an EFM (eight-to-fourteen modulation) signal component for digital audio, the portion marked B denotes a left channel FM signal component for analog audio, the portion marked C denotes a right channel FM signal component for analog audio, and the portion marked D denotes an FM signal component for a video signal.
In such a hi-fi video disk, the audio quality may be remarkably improved compared to the record reproduction of a audio signal by means of the FM modulation system since the dynamic range of a digital audio signal may be set at approximately 90 dB or more. On the contrary, however, the video band is determined by the width of the sideband area of the video FM signal. When the video band is made too wide, a bad influence is exerted on the reproduced video signal and the reproduced analog signal by the interference with the analog audio carrier. Therefore, it is difficult to set the band of the video signal at more than 4.5 MHz. Thus, the resolution is limited. Moreover, by the deviation of the duty ratio of a bit recorded on the disk, the audio FM carrier causes cross modulation with the video FM carrier and sometimes generates a beat in the reproduced signal.
The above explanation is expanded in the following paragraphs. Hitherto, the frequency bandwidth of a video signal (a luminance signal) in the baseband has been set at 4.2 MHz in the case of the NTSC system. Therefore, its spectrum is as shown in FIG. 2. Since such a video signal is frequency modulated and recorded within the range of 8.1 MHz to 9.3 MHz (7.6 MHz to 8.1 MHz for the synchronous signal), the lower limit frequency of a first sideband on the lower side of the video FM signal will be at approximately 3.9 MHz. Additionally, two carriers at 2.3 MHz and 2.8 MHz still lower than the lower limit frequency of the lower sideband are frequency modulated with a audio signal to thereby record two channels of audio signals which are frequency-division multiplexed and recorded together with the video FM signal. Furthermore, to comply with the demand for higher grade audio signals increasing with the popularization of the compact disk, audio signals are digitized by pulse code modulation (PCM) in the band lower than 1.75 MHz on the still lower side of the audio carrier at 2.3 MHz, and EFM-modulated audio EFM signals (PCM audio signals) are recorded. A spectrum of these video FM signals, audio FM signals and sound EFM signals is shown in FIG. 3.
FIG. 4 is a block diagram of a video disk player which reproduces such a video disk. A pickup 3 reproduces a recorded signal from a disk 1 which is rotated by means of a motor 2. The reproduced signal is amplified by an amplifier 4.
The output of the amplifier 4 is input to a high-pass filter 5 having a cut-off frequency at 3.5 MHz, whereby the video FM signal component is separated. The video FM signal is input to a demodulation circuit 6 and is frequency demodulated. The demodulated video signal is input to a low-pass filter 7, whereby unnecessary high frequency components of frequency over 4.2 MHz are eliminated. Furthermore, this signal is de-emphasized by means of a de-emphasis circuit 8 by the quantity corresponding to the known pre-emphasis quantity and is input to a processing circuit 9. The processing circuit 9 outputs a video signal modified with a predetermined processing.
A part of the output of the processing circuit 9 is also input to a separation circuit 10. The separation circuit 10 separates a predetermined control code signal (for instance, a 24-bit code) from the input signal and outputs it. This control code signal is inserted and disposed in, for example, a specific horizontal scanning line in the vertical retrace line period. A variety of controls are performed corresponding to the separated control code signal.
On the other hand, two band-pass filters 11 and 12 having center frequencies set at 2.3 MHz and 2.8 MHz separate respectively the two channels of audio FM signals from the output of the amplifier 4. Separated audio FM signals are input to two demodulation circuits 13 and 14 and are there frequency demodulated.
Besides, a low-pass filter 15 separates components below 1.75 MHz, i.e., the voice EFM signal. The audio EFM signal is input to a demodulation circuit 16, EFM demodulated, and separated into two channels of audio signals. These audio signals are output after further D/A conversion.
Either of the two channels of audio signals which are output from demodulation circuits 13 and 14 and two channels of audio signals which are output from the demodulation circuit 16 is selected by means of interlocking switches 18 and 19 and is output. A user may change over switches 18 and 19 as occasion demands.
A part of the output of the digital audio demodulation circuit 16 is also input to a separation circuit 17. The separation circuit 17 separates a sub-code signal from the input signal and outputs it. A variety of controls are performed corresponding to this sub-code signal.
Recently, the demand for better picture quality is increasing, and so-called high grade television broadcasting has been proposed. It has been also proposed that these high grade television signals are to be recorded on a video disk by the MUSE system. However, even if the luminance signal is compressed, a band of approximately 8.1 MHz is required in the case of the MUSE system. Therefore, it is required to change the existing standard in order to perform recording and reproduction by means of an optical video disk. When the standard is changed, however, the compatibility with a conventional optical video disk can no longer be expected.
In view of the foregoing, it is an object of the present invention to provide video signals of better picture quality while securing the compatibility with a conventional video disk.